Low pressure, high efficiency vapor compression distillation and product concentration devices are known in the art, principally through the prior work of the inventor herein both in his commercialization of these devices as well as his prior patents including U.S. Pat. Nos. 4,671,856; 4,769,113; 4,869,067; 4,902,197; 4,919,592; and 4,978,429, the disclosures of which are incorporated herein by reference. As shown in the inventor's '856 patent, a vapor compression distillation device is generally comprised of a first plate-type heat exchanger which preheats the feed liquid by transferring the heat from the distilled product and waste in a three fluid, fluid-to-fluid heat transfer process. A second plate-type evaporator/condenser heat exchanger has a plurality of plates defining a plurality of alternating boiling and condensing chambers having generally counter-cyclical flow, with a low pressure compressor for pressurizing the heated steam after it exits the boiling chambers and before it enters the condensing chambers. As explained and disclosed in the patent, the alternating boiling and condensing chambers are separated by plates which are desirably very thin to facilitate the transfer of heat therethrough. The plate pack construction includes precut neoprene or silicone gaskets which define the chambers and allow for internal manifolding which extends generally perpendicularly through the plates. Generally, fluid flow through the condensing chambers is in a vertically downward direction while in the boiling chambers, the feed liquid is maintained at a height to substantially cover the boiling surfaces such that steam created thereby generally flows outwardly towards the peripheral edges of the boiling chambers, and between pluralities of gasket members, to enter the steam manifolds. Thus, there is no strictly defined, unidirectional flow of steam from within the boiling chambers to the steam manifolds.
The device disclosed and claimed in the inventor's '856 patent is a good and valuable invention which has met with great commercial success. However, the inventor has continued his efforts to improve upon the breakthrough invention to render the process even more energy efficient and, hence, economical to operate.
Accordingly, there is disclosed and claimed herein, a new design for a vapor compression distillation device which provides significant advantages even over that provided by the inventor's prior invention as disclosed and claimed in the '856 patent. In his work, the inventor has determined that a truly perpendicular flow of fluid between the alternating condensing and boiling chambers provides tremendous advantages, especially when coupled with a uniform vertically upward flow of steam through the boiling chambers. A uniform, defined flow of fluid through each of the chambers provides dramatically improved performance as it eliminates the tendency, in a low pressure system, for pockets of vapor to form and inhibit full utilization of the plate surfaces for heat transfer. This phenomenon is akin to "vapor lock" which can lock up one or more chambers, or portions thereof, and prevent their operating as desired. With a strictly defined, uniform flow through each of the chambers, the entire plate surfaces separating the chambers is effectively swept to eliminate air pockets, vapor lock, or other inefficiencies from developing in the chambers.
Still another area of improvement in the design disclosed and claimed herein is achieved through the use of edge manifolds which directly feed each of the boiling and condensing chambers from between the outer edges or sides of the plates themselves. This construction completely eliminates the portal type or through manifolding found, for example, in the inventor's prior design. This construction eliminates right angle fluid turns in both the boiling and condensing chambers to thereby greatly reduce the amount of pressure required to force the fluid through the chambers. This provides a significant energy savings and eliminates points of pressure drop which impede operation of the system. Also, this direct manifolding eliminates the circuitous path which the vapor has to travel as it exits the boiling chambers, is compressed, and is returned to the condensing chambers. An example of a well designed and minimally disruptive path is found in the inventor's prior '856 patent. However, even with the inventor's prior design, evaporating vapor from one end of the plate pack was forced to make a right angle turn and traverse the entire length of the plate pack to reach the compressor and then nearly duplicate the same path to re-enter the condensing chambers. As will be appreciated upon reviewing the drawings and description contained herein, this path is greatly shortened and straightened in the inventor's latest design. Again, this feature provides increased efficiencies and reduces energy loss.
Still another aspect of the inventor's prior design which has been improved on is the plate design and the gasketing used to join the plates together and to the edge manifolds. For efficient plate heat exchanger operation, the individual plates are ideally as thin as possible in order to promote efficient heat transfer between adjacent chambers, are accurately spaced uniformly across the entire plate surface in order to promote uniform fluid flow through adjacent chambers, and are gasketed to correctly isolate and also communicate between chambers in a reliable manner. The inventor's prior design shown in the '856 patent includes plates which are separated by edge gaskets along with internal gasketing to define the chambers and also diffuse the flow of fluid between chambers and manifolds. While this gasketing arrangement worked quite well in the inventor's prior design, several areas of improvement have been focused on in achieving the design of the present invention. For example, the edge gaskets are typically glued and clamped in order to hold them in position between adjacent plates and seal the chambers contained therebetween. As such, the pressure inside the plate pack is exerted in a direction perpendicular to the sealing forces provided by the glue and the clamping. This arrangement is not ideally suited to resisting the internal forces between the plates. Still another feature of the inventor's prior design, and other prior art designs, includes expanses of adjacent plates which are not supported. In order to preserve the structural integrity, and achieve somewhat reliable uniform spacing, the thickness of the plate must be sized to span these distances. Of course, increasing the thickness of the plate is also undesirable in that it reduces the heat transfer between adjacent chambers.
In addressing these inherent limitations in prior art designs, the inventor herein has succeeded in designing and developing a new plate design and gasketing arrangement which provides a dramatic improvement in all of the aforementioned areas. In the inventor's new design, the periphery of each plate is corrugated, and a cross-hatched pattern of interrupted corrugations is formed across the surface of the plate. In assembling a plate pack, only one design need be used as the same plate is alternately reversed and the plates Joined and held under pressure. With this construction and assembly, the cross-hatch pattern of interrupted corrugations provides contact points between each adjacent plates throughout the interior chambers of the plates to thereby accurately locate the sidewalls of each chamber and also structurally support them at a reliable, uniform distance throughout the heat exchanger plate pack. As the plates are alternately reversed, the interrupted corrugations (which may be one of many designs) touch each other at a minimal point, ideally an infinitesimally small point, and there is virtually no interruption in fluid flow as the fluids traverse the various chambers in the plate pack. Also, as there is a definable area occupied by each interrupted corrugation, manufacturing tolerances are not critical to be maintained in order that the plates will still align as they are assembled in alternating fashion.
The continuous corrugations surrounding the periphery of each plate also serve to provide a plurality of contact points between adjacent plates for structural support and integrity of the plate pack. However, the inventor has succeeded in incorporating these corrugations into an edge sealing process which is uniquely distinct and provides many advantages over prior art edge gasket arrangements. As the plates are assembled into a plate pack by alternately placing one plate atop the other, a bead of liquid gasketing material, such as silicone, etc. as is known in the art, is applied along those edges of the plate where gasketing is desired. Then, as the next plate is laid atop the previous plate with this bead of gasketing material, the gasketing material is forced into a waffle-like pattern surrounding the various contact points previously mentioned, and thereby adhere to each of the adjacent plates. As can be appreciated, after the gasketing material has been cured it interlocks with these contact points to provide a seal which is held in place by the plates themselves and is mechanically reinforced in a direction directly opposite from those forces tending to push the gaskets out from between the plates. As might be expected, this waffle-like gasketing arrangement provides significantly improved resistance to gasket "blow-out". Indeed, the inventor anticipates that for some applications, the bonding forces provided by the gasketing material itself may be sufficient to hold this waffle-like gasketing in place. Nevertheless, the plate pack may also be conveniently bolted and pressurized to further secure this waffle gasketing. Not only does the inventor's waffle gasketing provide greater sealing capabilities, it significantly reduces the amount of waste previously created in making the peripheral gasketing utilized in his prior design. As can be appreciated, a peripheral gasket, when cut from a sheet of gasketing material, creates a center waste portion which can exceed the actual amount of gasketing which is utilized in the peripheral gasket itself. By forming and curing the gasket in place, virtually all waste is eliminated which dramatically reduces the cost for gasketing material for a plate-type heat exchanger.
While the principal advantages and features of the invention have been explained above, a more thorough understanding may be attained by referring to the drawings and description of the preferred embodiment which follow.